Familial polyneuropathy with anti-myelin-associated glycoprotein antibodies

Abstract

We describe the occurrence of the anti-myelin-associated glycoprotein (anti-MAG) syndrome, a well-recognized variant of chronic inflammatory demyelinating polyneuropathy (CIDP) with distinct clinical and electrophysiologic characteristics, in two brothers. A 70-year-old man presented with symmetric numbness distal to his knees, followed by progressive imbalance and gait unsteadiness that developed over 2 years. His similarly affected brother is described below (Case 2); there was no other relevant family history. On examination he had mild distal weakness in both lower limbs and symmetric vibration and proprioceptive loss distally in all four limbs. Muscle stretch reflexes were absent. Gait was severely ataxic and Romberg's sign was present. Nerve conduction studies revealed a severe demyelinating polyneuropathy with disproportionate distal slowing, prolongation of F waves without evidence of conduction block, and met criteria for CIDP.1 Immunoglobulin M (IgM) kappa monoclonal gammopathy was identified; IgM was 235 mg/dL (normal, 50 to 200 mg/dL) of which 50% to 90% was monoclonal and anti-MAG reactivity was positive at a titer of …